Electronic switching



Enme 27, EQSQ D. H. RANSOM ELECTRONIC SWITCHING 5 Sheets-Sheet 1Original Filed Feb. 7, 1946 INVENTOR. o/w/o H. IPA/VSOM BY I z ATTORNEYD. H. RANSOM ELECTRONIC SWITCHING June 27, 1956) Original Filed Feb. 7,1946 5 Sheets-Sheet 2 LOCK- \N PHAS a OSGLLATOR conmon m mo 50 Kc ICLIPPER 2%. 28 DIFFERENTIA- me cmculT AMPUHER INVENTOR.

'04 W0 H. mwson ATTORNEY J1me 1950 D. H. RANSOM 2,112,67

ELECTRONIC SWITCHING Original Filed Feb. 7, 1946 5 Sheets-Sheet 4 IN VEN TOR. 0/4 W0 H. FHA $0M BY I A T TORNZ'I' Y Original Filed Feb. '7,1946 5 Sheets-Sheet 5 INVEN T DAV/0 H fF/M/SOM A T TORNE Y Patented June27, 1950 UNETED YES rri c ELECTRONIC SWITCHING David Hiram Ransom,London W. C. 2, England,

assignor to Federal Telecommunication Laboratories, Inc., New York, N.Y., a corporation' of Delaware Original application February 7, 1946,Serial No.

646,169. Divided and this application December 11, 1947, Serial No.791,006

12 Claims.

phone system; Fig. 1 showing the subscribersline and common distributingequipment, Fig. 2 the line finder equipment and the talking circuit,Fig. 3 the line selecting and registering equipment, and Fig. 4 the dialpulse and ringing equipment.

Fig. 5 is a diagrammatic representation of a second type of electronicswitch that may be used in the system, and

Fig. 6 is aplan view of the screen used in said switch.

When a call is initiated at the substation l of one of the lines anegative potential is applied from battery 2 over a choke coil 3, awinding of a hybrid coil 4 associated with the line, and the subset tothe top dynode which is assumed to bear designation of a receivingdistributor which, together with a sending distributor 6, is provided incommon for a plurality of groups of subscribers lines which terminate inthe dynodes. In the system here disclosed it is assumed that there aretwenty lines divided into five groups. Any other number of lines may beprovided in any other grouping.

Distributors 5 and 6 are cathode ray tubes provided with the customaryelectron gun structures 8 and 9, the'dynode terminals of the lines andanodes, like 1, for collecting the secondary emissions of the dynodes.Only the control grid 5 0 of the sending tube 6 is utilized in thepresent case. The tubes are provided with deflecting means, such asplates It and I2, respectively, which are fed in multiple from a ZOO-kc.master oscillator I3 connected with the deflecting plates over a 50-kc.frequency divider M and a lG-kc. frequency divider l5, and a 90 phaseshifter 56.

Whenever the beam of cathode ray tube 5 engages the dynode #0 of thecalling line, electrons will fiow from the dynode to anode l of thistube and, therefore, a negative pulse 18 will be applied to the gridofcathode follower and inverter l9. The negative pulse in the cathodeoutput of triode I9 is fed to, the gr'dof clipper amplifier which isnormallybiased to draw current. The amplitude of the negative pulse 2|fed to the grid of this amplifier is so adjusted that it will drive thetube 26 beyond cut-off so that it will clip modulations by thetransmitter at substation I orby pulses produced by dial 22 in thecalling subscribers line. The plateoutput of clipper 20 consists ofpositive pulses 23 'fed to the grid of cathode follower 24 and throughthe cathode thereof to conductor 25 which ismultipled to the grids ofall the line finder gate tubes like 26 provided in the links throughwhich calling andcalled lines may be interconnected.

The line finder gate 26 is normally biased far enough beyond cut-off sothat the incoming signal 23 will not affect its plate output.

The line finder is provided with a lock-in oscillator 21 which operatesat a frequency slightly less than that of the master oscillator l3, anddivides this output to a'frequency of approximately 50 kc. which ispassed through a clipper and differentiating circuit 28 in the form of asharp positive pulse 29 to a multi-vibrator 30 arranged to synchronizeat approximately 10 kc. The square wave pulses 3| which appear in theoutput of 30 are differentiated in a network 32 and appear as pulses 33in the control grid of clipper gate 34. The constants and. bias of gate34 are so adjusted as to produce by'the leading edge of pulses 33 in theplate of a short square negative pulse 35 of approximately five.microseconds duration. The trailing edge of pulse 33 is suppressed. Thepulse is passed through, as 35, the cathode of a cathode follower 36, tothe cathode of the line finder gate 26. The amplitude of pulse 35 is soadjusted by a delay gain tube 31 that normally the line findergate 26 isnot driven beyond cut-ofi by the positive pulses 23 applied to itscontrol grid. Since the frequency of the line finder lock-in oscillator27 is slightly less than that of the master oscillator i3, the incomingpulses 23 and the local pulses 35 applied to the line finder gate willdrift-in time until they occur simultaneously, whereupon a negativepulse 39 will be produced in the plate circuit of the line finder gate26.

Pulse 39 will be passed through a rectifier 4! and an integrating netill to the grid of a gate control tube 42 to drive it beyond cut-off,whereupon a lock-in gate 43 will pass the signal to the lock-inoscillator 21, synchronizing the latter with the master oscillator IS. Aphase corrector 4 is provided between gate 43 land the oscillator 21 topermit accurate adjustment. 4

which is applied to the cathode of the line finder" gate as a pedestalpulse. The grid of gate 26 will be driven positive by the incoming pulse23, and clipping by grid current will occur.

The plate output 39 of the line finder gate is also applied over aconductor 45 to the control grid of an input gate control tube 46. Thetalking circuit has two input gate tubes 41, 48, .and two output gatetubes 49, 50 jointly controlled by the input control '46 and the outputcontrol tube 5|. The gate tubes are normally biased to cutoff on theirsuppressor grids which are connected in pairs to the plate resistors ofthe input and outputcontrxoltubes; those-f gates-41 and 59 to controltube 46 and those of gates 48 and '49 to output gate control 51. Thenegative pulse 39 drives the grid of gate control 46 beyond cut-offwhich reducesthe voltag drop across its plate resistor nal I8 25%. Theclipping action of triode 20 will cut off the modulated portion so thatthe pulses 23 applied to the line finder gates 26 will be uniform.However, a clipper tube 52 to which positive pulses 53 appearing in theplate output of inverter [9 are applied is biased so that only themodulated portion of the pulse 53 will appear as negative pulses 54 inits pl'ate circuit. Pulses 54 are applied to the grid of cathodefollower 55 and are transmitted over conductor 56 to the control gridsof the input gates 41, 48 of all the links.

Normally a series of negative pulses 55 will be passed by the input gate41 to the dial pulse circuit over conductor 6| before the subscriberstarts dialing. The selective action of the input clipper tube 52 willinterrupt these pulses with each pulse produced by the callingsubscribers dial .22. A low pass filter in the grid of amplifier tubeE!) to which the output circuit of gate 41 is connectedover conductorl6] forms positive pulses 62 appearing therein into l'ow frequencypulses which, after amplification, are integrated at 33- and shaped inclipper tubes 64 and 65 to form square wave nega- The bias of the unitand group dialing gates 69,

H is so adjusted that the leading edge of pulse 68 is suppressed and thetrailing edge passed as a negative pulse 12 from the plate of unit dialgate 69 over conductor 13 to the units register circuit (Fig. 3), and asnegative pulse 14 appearing in the plate of group dial gate "II overconductor l to the group register circuit (Fig. 3). The pulses l2 and Mare passed only when the screen grids of the unit and group dial gatesare positively biased.

Triode 16 of an Eccles-Jordan group digit-trigger circuit is normallyconducting and biases the screen grid of unit gate 69 near zero and thescreen of the second digit.

grid of grid dial gate H at positive potential. The suppressor grids ofthe two dial gate tubes 69 and "H are connected in multiple and held atzero. bias by the units digit trigger circuit com- 32 which, togetherwith a'triode 83, constitutes a digit pulse flip-flop circuit. The firstpulse 66 of a train will transfer conduction from 82 to 83 and thecircuit constants will maintain this condition until the end of a seriesof pulses, where upon 32 will again become conducting.

At the end of the first series of dial pulses when 83 is again cut-off,a positive pulse will be sent from its plate over a differentiatingcircuit 84 to. a digit control flip-flop circuit comprising tubes 85 and8B,'the latter normally conducting.

The pulse will transfer conduction to tube 85 for a period of timedetermined by the constants of the circuit and a negative pulse 81 willbe sent to the group digit control tubes to transfer conduction fromtube 16 to H. r

The screen grids of the of the two dial gate tubes 69 and H beingconnected to the plates of 16 and TI, respectively, first, as abovedescribed,

only the group dial gate H and then only the unit dial gate 69.

These gates will in turn pass first the pulses M to the group registersand then the pulses 12 to the unit register. v

After the dialing of the second or units digit, a negative pulse 81 sentfrom the digit control 85, 83 will flip the group digit gate so that T6will again become conductive and will send out a pulse to the unitsdigit control 18, 19 to transfer conduction from '19 to 13. Tube 18 willnow bias the suppressor grids of both dial gates 69 and H to cut-off toprevent transients from affecting the setting of the registers.

The tube 78 will apply also a bias over conductor 88 t0 the suppressorgrid of an output gate tube 89 to permit the passage of a ringingsignal, aswill be explained below.

A negative pulse is sent from the plate of 18 over a conductor 90 to aringing control trigger v circuit comprising triodes 9| and 92, with theformer normally conducting. The ringing control circuit contains also a,ringing gate 93 which is biased to cut-off until the completion of thedialing when, as above stated, through the agency of the units digittrigger circuit the ringing control tube 9| is made conductive. Thiswill so bias the control grid of the ringing gate 93 as to make itconductive. Ringing current generated by an oscillator 94 modulates thesuppressor grid of the gate 93 and produces pulses in the plate of thegate 93 which are applied over a conductor 95 to the control grid of theoutput gate 49.- Whenever the output gate is functioning, pulses 96 willbe applied through an amplifier 91 to the control grid of the outputgate 89 whose output circuit is connected over conductor 98 with thecontrol grid ll] of the sending distributor 6. This will cause theringing of the called line over distributor 8, because the suppressorgrid of 89 is opened when the beam of distributor 5 sweeps the dynode ofthe called line.

The group and units registers are conventional trigger circuitsconnected as binary counters and arranged to receive and store fivedifferent digits representing the group or tens designations of thecalled lines. Obviously, provision may be made for any other grouping.

Each register comprises a pair of tubes, such as-I00, "3!, I02, I03,I04, I05, I06 and I01, of which the even numbered tubes are normallyconducting. The first group dial pulse I4 which arrives over conductorI5 will cause the #1 group register to flip conduction from tube I84 totube I05. This in turn will apply a potential over conductor I08 to thecontrol grid of a group selection tube I09 to make it conductive.

The next group dial pulse 14 arriving over conductor 75 will restoreconduction to tube I05 which will cut-off the selection tube I09 andpass the pulse to group register #2 over conductor H making I07conductive. A pulse will now be passed from the #2 group register overconductor III to operate group selection tube H2.

A third pulse 14 which arrives over conductor '15 will again cause the#1 group register to function and operate the group selection tube I09,the group selection tube H2 having been cut off in the meantime.

The fourth pulse 14 over conductor I restores both the #1 and the #2group registers to normal but will be applied over conductor H3 tooperate the #4 group register H4 (which is like the two other groupregisters). This group register in turn will operate over conductor I I5a group selection tube I I 6.

The fifth group dial pulse I4 arriving over conductor against operatesthe #1 group register and therethrough the group selection tube I09.

It will be seen therefore that if the first or group digit is 1, thentube I09 is operated, if it is 2, then tube H2, if 3, then I09 and H2,if 4 then tube H6, and if 5, then tubes H6 and I09.

After the change-over controlled by elements 8i to 83, the units pulsesI2 arriving over conductor I3 will affect the #1 and #2 units registersin the same manner as was described in connection with the groupregisters. Similarly, the units registers over conductors I I I and H8will operate units selection tubes H9 and I in the same manner as thegroup selection tubes were operated under the control of the groupregisters. The two units registers and selection tubes make possible theselection of one out of four lines in each of the five groups.

Upon the completion of the dialing, the odd numbered tubes in certain ofthe registers will be conducting. If, for example, the called line #32were dialed, then the #1 and #2 group registers and the #2 unitsregister would be operated, operating in turn the group selection tubesI09 and H2 and the units selection tube I20.

The plates of these selection tubes are connected to common resistancesI2I and I22, respectively. When one of the register trigger circuits isflipped to its operating condition, it will bias its associatedselection tube to draw more current, and the amount of current drawn bythe tube will depend upon the resistance in the cathode circuit of thetube and the positive bias applied to its grid. 'By properly adjustingthe cathode resistors I23, I24, I25, I26 and I21 of the selection tubes,the current flowing through the tubes can be made to vary in intervalsteps. For example, the cathode resistor I23 of tube I09 may beadjusted, so that one milliampere of current will flow through the tubewhen positively biased, the resistor I24 so that two milliamperes willflow through the tube H2 when positively biased, and I25 so as to permitthe flow of four milliamperes through tube I I6 when its grid ispositively biased. The current in the output circuit is applied overconductor I21 to control the operation of the two electronic switchingdevices I28 and 228, two embodiments of which will now be described withreference to Figs. 5 and 6.

In the electronic switch of Figs. 5 and'6,"a cathode I29 is heated by afilament I30 to emit electrons which are controlled by a grid I3I. Theelectrons that pass through grid I3I are formed into a beam by anodesI32, I33 and I34. The beam is constrained to sweep along a circular pathby means of the customary horizontal and vertical deflecting plates I35.The potentials are so adjusted as to direct the beam between thetoroidal electrodes I36 and I31 of a condenser. The potentials on thesecondenser plates can be adjusted so that the beam will sweep in circlesof any desired radius on a screen I38.

'As shown in Fig. 5, the screen I38 has angularly and radially displacedcut-out segments I39, I40, MI and I42. The dynodes I43 are aligned withthe cut-outs. Secondary electrons deflected by the dynodes are picked upby a positively charged anode I44 which has extensions (not shown)operating as shields between the individual dynodes I43.

With the four cut-outs I39-I42 in screen I38, the switch will have a,time division of four. However, any other number of cut-outs may beprovided.

The signal may be taken off the screen I33, the anode I44, or thedynodes I43. The potential applied to the grid I3I may be used tomodulate the beam. The variations in dynode potential will modulate theanode I44 and, conversely, the variations in the potential applied tothe anode I44 may be used to modulate the output of the dynodes I43 whenthe beam sweeps over them.

The switch may be used to afford time division in a multiplex system,the beam being rotated at the recurrence frequency. By adjusting thepotential on the condenser plates I36 and I31, any channel may be chosenand connected with its assigned. terminal I43, affording a two-waycommunication since the grid I3I may be used to modulate the dynode I43and the dynode in turn can be used to modulate the anode I44.

If the number of channels is too great for separation within one tube,then two or more tubes may be connected in tandem. For example, thefirst monoscope would have a circular sweep frequency at the repetitionrate and ten cut-outs dividing the time diameter into groups of ten. Theoutput would be taken off the anode I44 and fed to the grid I3I of thenext tube which sweeps at ten times the group frequency and also has tencut-outs in its screen. By applying a potential on the toroidalcondenser I36, I31 in each tube, the desired time channel can beselected.

If his desired to mark the occurrence ofany event in a "cycle of thesweep frequency, this can be done in one or more of the tubes- Two ofthe switches of the type shown in Fig. 6 are used in the registering andselecting circuit of Fig. 3, and will be referred to as group monoscopeI28 and units monoscope 228. The monoscope I28 bears the same referencenumerals as in Fig. 3, and the monoscope 228 the corresponding numeralsin the two-hundreds.

The beam of the group monoscope I28 is deflected by integral steps togive the correct timing pulse period. The beam of the units monoscope228 is rotated at 50,000 times per second. The screen 236, which servesalso as an anode, is divided into segments of one-quarter the total sothat four deflection voltages will give four different input signals.These signals are transferred from the dynode 243 of the units monoscopeto the grid I 3| of the group monoscope I28 which is rotated at 10,000times per second and as five time divisions. During each of these timedivisions, the four units time divisions of monoscope 228 can betransmitted. Hence, if proper voltage is applied to the toroidalcondenser plates I36, I31 and 236, 231, any desired group and unitsselection can be performed. Pulses I45 produced in the dynode I43 of thegroup monoscope I 28 are applied to the grid of an inverter and cathodefollower I46. The anode output of I46 is applied over conductor I 41 tothe suppressor grid of a pentode I 48 controlling the tripping of theringing current by allowing the passage of a pulse through tube I69 tothe control grid of the ringing gate 93.

When the called subscriber answers, pulses will be generated in thecircuits associated with the receiving tube 6 in substantially the samemanner as described in connection with the initiation of the call. Thesepulses are then passed through the cathode follower and inverter 9 tothe clipper amplifier 20, cathode follower 24 and then from the cathodeof 24 over conductor I49 to the control grid of the trip ringing tubeI48. The negative pulse appearing in the output circuit of the tripringing tube I48 transfers conduction in the ringing control circuit totube 92 and biases the ringing gate 93 to cut-off. The application ofthe ringing current from the oscillator 94 is thus stopped and thesubscribers are ready to talk. v

The cathode output of the inverter and cathode follower I46 is appliedover conductor I50 to a busy pulse shaper II and therethrough to thegrid of a busy gate I52 to cancel positive pulse 23 by a negative pulseI53, thus to prevent a second line finder gate like 26 from operatingwhen the called line answers.

The pulses on conductor I50 are applied also to the control grid of theoutput gate control tube 5|. This tube controls the suppressor grids ofthe input gate 48 and output gate 49.

A two-way talking circuit is now established between the calling andcalled lines. From the called subscribers line, voice modulated signalsare passed through the receiving distributor 5, the cathode follower andinverter I9, clipper 52, cathode follower 55, conductor 56, to thecontrol grid of the input gate 41. Whenever the suppressor grid of thisinput gate is opened by the control tube 46, the pulse is passed throughthe gate 41 and a low pass filter I54 to the control grid of output gate49. When the control tube 5I opens the output gate, the pulse is passedthrough amplifier 91, the output gate 89 and conductor-98 to the gridIII of the sending distributor 6, whose beam :is at this instant on thedynode in which the called line terminates. In the called line themodulated pulse goes through hybrid coil 4 to operate the receiver inthe subset.

The path of the modulated speech signals from the calling subscribersline to the called line is the same as above described, except that thesignal is fed through input gate 48 and a low pass filter I55 to'thecontrol grid of the output gate 50.

Upon the termination of a call, when the calling subscriber hangs up thevarious circuit elements are released under the control of the delayedgain tube 31. The register circuit and the dial gates which arelocked-in are released under the control of tubes I56, I51 and I58. Thetube I56 is normally conducting. When the calling subscriber starts tocall, the delayed gain tube transmits through its cathode and aconductor I59 a pulse to the grid of release control tube I5! andthrough the plate thereof to the grid of I56 to operate the latter forthe duration of the call. When the calling subscriber hangs up at theend of the conversation, tube I51 again operates and applies a negativepulse to the grid of the release tube I53 which, b-y-sending a positivepulse over conductor I60 and the conductors I6I and I62 connectedtherewith, will release all registers and storing circuits to normal.The link is now ready for the transmission'of a new call.

What is claimed is:

'1. In an electronic switching device, means for producing a beam ofelectrons, a plurality of electrodes, a screen having a plurality ofopenings through which an electron beam may pass to impinge on thedifferent electrodes, each opening defining an arc of a circle, eachopening having a different radius measured from a central point, eachopening angularly displaced from the others and disposed about saidcentral point, and means for deflecting said beam to impinge on adesired electrode through the'openings in said screen through thescreen.

2. The device according to claim 1, wherein one of said electrodescomprises a grid, said grid adapted for modulating the beam.

3.'The device according to claim 1 wherein one of said electrodescompresses an anode, and means for applying potentials to the electrodesto modulate the current flowing in said anode.

4. The device according to claim 1 wherein one of said electrodescomprises an anode, and means for applying potentials to said anode tomodulate the electrode current.

5. The device according to claim 1, and a load connected with eachelectrode.

6. The device acording to claim 1, wherein said means for deflectingsaid beam comprises a condenser having plates affording a toroidalopening through which the beam passes.

'7. The device according to claim 1, and in which the screen hasangularly and radially displaced slots through which the beam mayimpinge on the electrodes the radial displacement of each of said slotsbeing different.

8. In an electronic switching device, means for applying a potential tosaid device, means for producing a beam of electrons, means for causingsaid beam to describe a circular path, a condenser having two electrodesaffording a toroidal opening through which said beam may pass, anelectrically conductive screen having angularly and radially displacedcut-out segments, dynodes aligned with said segments to be impinged uponby the beam during its rotation, and an anode for collecting secondaryelectrons emitted by the dynodes.

9. A device according to claim 8, and means for varying said potentialon one of the condenser electrodes to cause said beam to pass through acertain segmental cut-out and impinge on the dynode in registrytherewith.

10. A device according to claim 8, and a grid for modulating the beam.

11. A device according to claim 8, and means for varying the potentialsapplied to the dynodes to modulate the anode current.

12. A device according to claim 8, and means for varying the potentialapplied to the anode for modulating the dynode current.

DAVID I-IIRAM RANSOM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

